Engine Configuration

engine.yaml is the sole configuration surface for an engine — no code changes needed to add a new variant or adjust parameter handling. For the crate structure and how to build a custom engine binary, see Engine Internals.

Starting an Engine

metis-engine-generic server --engine-config /etc/metis/engine-config.yaml

Set the three required environment variables:

DATABASE_URL=postgres://user:pass@host:5432/metis
REDIS_URL=redis://:pass@host:6379
NATS_URL=nats://user:pass@host:4222

Parameter Fields Reference

Field	Type	Required	Description
names	[string]	yes	All accepted aliases. First is canonical.
cliFlag	string	yes	Flag written to the CLI command
type	string	yes	string, int, bool, list
default	any	no	Value used when client omits the parameter
strictDefault	bool	no	If true, always use default, ignore client value
required	bool	no	Reject run if missing and no default
listSeparator	string	no	Separator for list type (default ,)
booleanStyle	string	no	flag (presence) or value (-flag true)
sensitive	bool	no	Redact value from logs; pass via envVar
envVar	string	no	Environment variable to set (requires sensitive: true)
validate	[ValidationSpec]	no	List of validation rules

Validation Types

Type	Fields	Description
enum	allowed: [string], message	Value must be in allowed list
regex	pattern: string, message	Value must match regex
range	min: int, max: int	Numeric value must be within range
file_exists	—	File must exist on the engine host filesystem
file_extension	allowed: [string]	File path must end with one of the allowed extensions

Denied Parameters

Denied params are evaluated against the raw keys sent by the client before alias resolution.

Field	Values	Description
pattern	string	The pattern to match against
type	exact, regex	Match mode
reason	string	Error message returned to client

workflowParams Methods

Method	Behaviour
inline	Parameters appended directly to the CLI command as flags
file	Parameters written to a temporary params file; path substituted into {workflow_params} in the command template

Registering a New Engine

The engine registers its heartbeat in Valkey and appears in GET /service-info. Submit runs using a workflow_engine that matches engine.name. For custom parsing or log handling, implement the Engine trait and build a custom binary. See Engine Internals → Adding a Custom Engine.